Temporal and Spatial Distribution Patterns and Traceability Analysis of Furfural and Furfuryl Alcohol in the Brewing Process of Sauce-Flavor Baijiu

In this study, liquid-liquid microextraction coupled with gas chromatography with hydrogen flame ionization detection (LLME-GC-FID) and orthogonal partial least squares-discriminant analysis (OPLS-DA) were integrated to track and monitor the contents of furfural and furfuryl alcohol in the raw materials, Daqu, stacking fermented grains, pit fermented grains, upper and lower steamer fermented grains, and distillates, which were collected at the key steps of the brewing process of sauce-flavor Baijiu. The results showed that the spatial and temporal distribution of furfural and furfuryl alcohol during the brewing process of sauce-flavor Baijiu varied significantly. The contents of furfural and furfuryl alcohol increased at first and then decreased at the Daqu-making stage. The contents of furfural and furfuryl alcohol showed an upward trend at the stacking fermentation stage. During the pit fermentation stage, the content of furfural decreased while the content of furfuryl alcohol increased. During the distillation process, the content of furfural increased, while the content of furfuryl alcohol decreased from the upper steamer to the lower steamer. The contents of furfural and furfuryl alcohol showed an increasing trend at the alcohol extraction stage. The distribution of furfural during the brewing process was generally lower layer > middle layer > upper layer. The distribution of furfuryl alcohol was middle layer > lower layer > upper layer at the stacking fermentation stage, and lower layer > middle layer > upper layer at the cellar fermentation stage and the distillation stage. Traceability analyses showed that furfural and furfuryl alcohol were mainly derived from Daqu powder, rice husk, and the late distillation stage. The formation mechanism of furfural during the brewing process of sauce-flavor Baijiu was attributed to microbial action, sugar degradation, and Maillard reaction under high temperature and acidic conditions. This study provides theoretical guidance for the reduction and control of furfural and furfuryl alcohol during the brewing of Baijiu, and provides a scientific basis for regulating the quality and safety of Baijiu.